1. Field of the Invention
The present invention relates generally to radar used for tracking multiple targets. More specifically, the present invention relates to a monopulse radar tracking method which analyzes boresight error information to determine a location for multiple targets.
2. Description of the Prior Art
Monopulse radar is widely used as a military tracking radar because of its high accuracy and relative immunity to electronic countermeasures that degrade other tracking radar and their associated methods of tracking. Monopulse radar uses a single RF (radio frequency) pulse to gather angle information, as opposed to directing multiple narrow-beam pulses in different directions and looking for a maximum return to identify the target.
As shown in FIG. 1 monopulse antenna 20 is divided into four quadrants TR (top right), TL (top left), BL (bottom left) and BR (bottom right). A target 22, which is an RF reflector, directs a reflection of the single RF pulse at the four quadrants of antenna 20 which is represented by the vectors 23, 24, 26 and 28. The radar's signal processing circuitry then calculates the boresight error for the signal by finding its sum signal, its pitch Delta signal, and its yaw Delta signal.
The sum signal is TLv+TRv+BLv+BRv where the terms TLv, TRv, BLv and BRv represent voltage vector summations in each of the four quadrants of the antenna 20. The pitch Delta signal is (TLv+TRv)−(BLv+BRv) and the yaw Delta signal is (TLv+BLv)−(TRv+BRv).
The boresight error in each axis (Pitch and Yaw) is (Del.Cross.Sum/Sum.Dot.Sum) where Del.Cross.Sum is a cross product and Sum.Dot.Sum is a dot product.
The boresight error information then indicates the angle of target 22 within the radar beam. When there are two targets the averaged boresight error information indicates the angle of arrival of the dominate target. There is, however, a need to utilize the boresight error information to locate the second target.